The invention relates to luminaires including arc tube lamps such as metal halide high intensity gas discharge lamps and, more particularly, to a luminaire including a heater for heating the lamp arc tube prior to starting the lamp.
High intensity gas discharge (HID) lamps are employed in a wide variety of applications including street lighting, industrial lighting, and lighting for sporting events. A disadvantage of high intensity gas discharge lamps is that they in general cannot be turned off and on quickly or frequently. For example, in order to reduce power consumption, it is desirable to turn lamps off when light is not required. For sports lighting applications, it is desirable to produce theatrical effects such as introducing players into a darkened arena with a spotlight on a particular player, and thereafter turning the arena lights back on.
There are however several fundamental problems associated with the operation of HID lamps. One fundamental problem is that the starting process for a high intensity gas discharge lamp normally causes damage to the lamp such that light output is slightly reduced for each start. Thus, high intensity gas discharge lamps are generally rated to operate for ten hours per start, and any reduction in the on period usually results in significant Lamp Lumen Depreciation. Another fundamental problem is that high intensity gas discharge lamps require a warm-up period, and it may take several minutes for the light output to reach even 90% of the fully warmed-up level. In an industrial lighting application, turning off lamps when light is not required likely would reduce the on-periods to less than ten hours per start. Moreover, adequate illumination may not be provided for the first several minutes after lamps are started. These problems can be exacerbated in sports lighting applications.
One general way the above-mentioned problems can be minimized is by preheating the arc tube, prior to starting. Preheating the arc tube decreases the amount of damage done by starting, and additionally reduces the warm-up time. One known technique is to provide a heater for the arc tube, such as is disclosed in Collins et al U.S. Pat. No. 5,898,273.
Another technique, closely related to preheating, is to dim a metal halide HID lamp by operating it at reduced power, such as one-half power, as is done in commercially available bi-level systems. When full power is subsequently desired, the arc tube has in effect been pre-heated. Nevertheless, disadvantages remain. Operating the lamp at a reduced power level still consumes a significant amount of power, and Lamp Lumen Depreciation occurs even in dimmed mode. Metal halide HID lamps tend to be inefficient and produce a poorer quality of light in the dimmed mode (degraded color temperature and color rendering index).
Also, both approaches result in light output from the luminaire in situations where a more darkened luminaire would be desirable for theatrical purposes. A preheater such as is disclosed in Collins et al U.S. Pat. No. 5,898,273 is an incandescent heat lamp, which also produces visible light. A dimmed lamp in a bi-level system produces illumination (which may be intentional and desirable in some applications).
Deserving mention in the context of the invention is an entirely different prior art approach, particularly in sports lighting applications, which is to employ a mechanical shutter system to block the light from the luminaire. An example is disclosed in Payne U.S. Pat. No. 5,887,970. Opening the shutter provides xe2x80x9cinstantxe2x80x9d light. Mechanical shutter systems have the disadvantage of heat build-up while the shutter is closed, and do not in any way address the desire to reduce power consumption by turning lamps off when not in use.
It is therefore seen to be desirable to provide a luminaire including an arc tube preheater, in which visible light from the arc tube preheater is minimized.
In an exemplary embodiment, a luminaire includes an illumination reflector having a forward, light-projecting open end and a rear apex. An arc tube containing an ionizable fill and a pair of electrodes is mounted in front of the rear apex. At least a portion of the illumination reflector is a dichroic element which is relatively reflective of visible light and relatively transmissive of infrared radiation. A source of infrared radiation is located outside the illumination reflector for directing infrared radiation through the dichroic element portion of the illumination reflector to heat the arc tube.
Thus, the arc tube can be preheated to improve Lamp Lumen Depreciation, and to allow higher initial light levels after turn-on and faster warm-up. The location of the source of infrared radiation outside the illumination reflector minimizes the amount of visible light from the source of infrared radiation which enters the interior of the illumination reflector, allowing the luminaire to appear relatively dark during preheat. Heating of the arc tube can be accomplished either prior to initial starting of the arc tube, or after the arc tube lamp has been in operation and is turned off prior to a re-start. The terms xe2x80x9cpreheatxe2x80x9d and xe2x80x9cheatxe2x80x9d are employed herein interchangeably, and are intended to refer to either circumstance.